An obscure electrical phenomenon has a profound influence on our atmosphere. This field, known as the ambipolar electric field, has finally been measured by scientists.
Thanks to a NASA rocket, the existence of this field has been confirmed, revealing its key role in the atmospheric escape above the poles.
The geographic North Pole as seen from the Endurance mission at an altitude of 477 miles (768 kilometers) above the Arctic. The faint red and green streaks at the top of the image are lens artifacts. Credit: NASA
Discovered with the help of the Endurance mission, this electric field could be as fundamental as gravity or magnetism for our planet. It directly influences the escape of Earth's atmosphere above the poles. Understanding this mechanism helps clarify the evolution of our ionosphere.
Since the 1960s, scientists have suspected the existence of such a field. They observed a mysterious "polar wind," a stream of particles leaving Earth's atmosphere at supersonic speeds, without apparent heat. To explain its origin, a weak but extended electric field was hypothetically proposed.
Attempts to detect this field were, until now, impossible with available instruments. It was only in 2016 that Glyn Collinson's team at NASA's Goddard Space Flight Center developed a device capable of detecting this field.
On May 11, 2022, the Endurance mission was launched from Svalbard, a Norwegian archipelago near the North Pole. At its peak of 477 miles (768 kilometers), it captured a potential difference of just 0.55 volts. This weak field is nonetheless sufficient to explain the polar wind.
Hydrogen ions, the lightest and most abundant in this wind, are propelled at supersonic speeds, defying Earth's gravity. This field also increases the density of the ionosphere far beyond what it would be without it.
These discoveries open new avenues for exploring atmospheric evolution not only on Earth but also on other planets. A similar field could exist on Mars and Venus, influencing their atmospheres in comparable ways.
What is the ionosphere?
The ionosphere is a layer of Earth's atmosphere located between 37 and 621 miles (60 and 1,000 kilometers) in altitude. It is composed of ionized particles, meaning electrically charged molecules and atoms. These particles are primarily created by solar radiation stripping electrons from molecules.
This layer plays a crucial role in the transmission of radio waves, as it can reflect signals, allowing them to propagate over long distances. Additionally, the ionosphere protects Earth from harmful solar radiation by absorbing some of the ultraviolet and X-ray radiation.
The ionosphere is also the setting for spectacular phenomena such as polar auroras, which result from the interaction between charged particles from the solar wind and those in the ionosphere, creating colorful lights in the skies of polar regions.